A group called "ModMyEee" created a release of Windows 7 RTM candidate build 7264 specifically for netbooks. To quote: "The Eee7 is a special version of Windows 7 Ultimate, based on the last edition 7264, made by the group "ModMyEee". It occupies only 1.49 GB of space on an installation USB drive and 4 GB when installed on the hard disk. It operates on any netbook and is faster than XP SP3! No major functionality has been removed; all networking capabilities remained intact, as does dardware support." Note: It’s un-official version.
More info: Download